Control system of rotary kilns

ABSTRACT

In a control system of a rotary kiln of the type comprising a power detector for measuring the driving power of the kiln and the output signal from the power detector is utilized to control the kiln, there is provided a synchronizing signal generator for generating one synchronizing signal during one revolution of the kiln, an integrator responsive to the synchronizing signal for integrating the output signal from the power detector for an interval corresponding to one revolution of the kiln, and a memory for storing the output signal from the integrator for use it for the control of the kiln.

United States Patent 1 1 $729381 Itoh et al. 5] Apr. 24, 1973 [5 CONTROL SYSTEM OF ROTARY 3,578,298 5/1971 Hurlbut et al. ..263/32 R KILNS 3,606,284 9/1971 Hurlbut et al ..263/32-R [75] Inventors: Tsutomu Itoh, Tokyo; Koji Suga, Chiba-shi; Yasuo Takumi, Tokyo; Masahiro Yamamoto, Chiba-shi, all of Japan [73] Assignee: Onoda Cement Co., Ltd., Onoda-shi,

Yamaguchi-ken, Japan [22] Filed: Dec. 28, 1970 21] App]. No.: 102,027

[30] Foreign Application Priority Data Dec. 28, 1969 Japan ..44/105088 [52] us. Cl. ..340 220, 340/236, 340/420, 106/100, 432/37, 432/45 [5 l Int. Cl ..F27b 7/20 [58] Field of Search ..263/33, 32

[56] References Cited UNITED S TATES PATENTS 1,731,809 l0/l929 Bendy ..263/33 R Primary ExaminerJohn J. Camby Atl0rney-Km0n, Palmer & Estabrook [57] ABSTRACT In a control system of a rotary kiln of the type comprising a power detector for measuring the driving power of the kiln and the output signal from the power detector is utilized to control the kiln, there is provided a synchronizing signal generator for generating one synchronizing signal during one revolution of the kiln, an integrator responsive to the synchronizing signal for integrating the output signal from the power detector for an interval corresponding to one revolution of the kiln, and a memory for storing the output signal from the integrator for use it for the control of the kiln.

7 Claims, 8 Drawing Figures DRIVING SIGNAL DETECTOR l? INTEGRATOR 48 MEMoR Y 20 Patented April 24, 1973 4 Sheets-Sheet l POWER DETECTOR FIG. 5

DR RIN FIG. 2

RP VAR F TIME ONE ION OF KILN Patented April 24, 1973 4 Sheets-Sheet I3 DETECTOR I NTEGRATOR FIG. 6

FIG. 7

R O O 2 M m m g m m2 R M. m a B W 2 R M E E T M N Ill 1 m R 0 i m M m Ah E W8 M E II T W CONTROL SYSTEM OF ROTARY KILNS This invention relates to a control system of a rotary kiln and more particularly to an improved control system of a rotary kiln for detecting the internal condition of the kiln.

In the operation of a rotary kiln, more particularly a rotary kiln utilized to fire cement clinker it has been the practice to measure the power consumption of the driving motor of the rotary kiln to determine the condition of movement of the raw material in the kiln as well as the progress of the firing condition. However, most of the power is consumed to rotate the kiln itself, the quantity of power that varies dependent upon the internal condition of the kiln is only a small fraction of the total power and in addition such variable power component contains large noise component. Accordingly, when the operator controls the kiln by judging its internal condition from the signal representing the variable power component it is extremely difficult to accurately determine the internal condition from the information provided by such signal containing a large quantity of noise, thus requiring a highly skilled operator. Moreover, such judgement greatly is affected by the personal skill and fatigue of the operator. If one tries to use the signal representing the variable internal condition to control the kiln through an electronic computer it will require a large cost of installation. Moreover, as the noise component of the signal is produced at each revolution of the kiln which normally is rotated at a speed of one or two revolutions per minute it is not permissible to directly introduce such a signal containing large noise component into the computer for performing the process control of the kiln. For this reason, it has been required to develop a novel device capable of extracting an effective signal alone for the effective control of the kiln out of the signal containing a large noise component. By measuring the driving power of the kiln it is possible to determine the following information from the result of measurement:

a. dropping of the ring of the clinker adhered to the inner wall of the kiln and the rushing of the not yet fired raw material through the kiln;

b. presumption of the degree of firing of the clinker inside the kiln.

Detection of the information regarding the phenomenon a should be made as fast as possible because it involves a phenomenon which varies very quickly.

In the past, since the detection of this phenomenon was made by observing the clinker at the outlet end of the kiln a long lag was unavoidable. On the other hand, as the information regarding the phenomenon b concerns the firing condition and its speed of variation is very low, it is necessary to extract only the correct and efficient signal by thoroughly attenuating the noise component in order to extract an available signal out of the measured signal containing a large noise component. Although a time constant type filter is suitable for the extraction of the useful signal, such a filter is not suitable for the extraction of a rapidly varying signal such as a. Accordingly, it is extremely difficult to simultaneously extract two signals representing a and b of opposite natures.

It is an object of this invention to provide a novel control system of a rotary kiln wherein the control is performed by determining an information regarding a phenomenon which varies rapidly and hence is required to be determined rapidly an information regarding a gradually and steadily varying phenomenon.

A further object of this invention is to provide a novel control system for a rotary kiln according to which the driving power of the kiln is measured to extract a useful signal corresponding to the variation in the internal condition of the kiln from the measured value containing a large noise component, and the extracted signal is used for the control of the kiln.

Still further object of this invention is to provide an improved control system of a kiln capable of correctly detecting a useful signal having a large degree of noise attenuation.

According to this invention there is provided a control system ofa rotary kiln comprising a power detector for measuring the driving power of the kiln, a synchronizing signal generator for generating at least one synchronizing signal during each one revolution of the kiln, an integrator responsive to the synchronizing signal for integrating the output signal from the power detector for an interval corresponding to integer multiple revolutions including one of the kiln, a memory for storing the output signal from the integration circuit, the stored signal being read out as a control signal.

The present invention can be more fully understood from the following detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of the novel control system for a rotary kiln, partly in perspective view and partly in block connection;

FIG. 2 shows signal diagrams respectively representing (a) a rotating speed of kiln (b) an input power of driving motor and (c) an output from an integrator;

FIG. 3 is an enlarged view of a portion of the waveform shown in FIG. 2(b);

FIG. 4 is a block diagram of the kiln driving signal detector shown in FIG. 1;

FIG. 5 is a block diagram of a modified kiln driving signal detector;

FIG. 6 shows an electrical connection of the memory shown in FIG. 1;

FIG. 7 is a view similar to FIG. 1 showing a modified embodiment of this invention; and

FIG. 8 shows waveforms to illustrate how to derive out a driving signal utilized in the control system shown in FIG. 7.

As shown in FIG. 1, a cylindrical rotary kiln 11 is installed slightly inclined. Raw material 12 of the cement clinker is admitted into the kiln 11 through its upper or right hand end and is fired by the heat supplied from a heat source, not shown. The kiln is rotated at a low speed of about one to two revolutions per minute by a driving device 13 for moving the raw material 12 toward the lower end or exit end while stirring the raw material. The driving device 13 comprises a gear 15 driven by an electric motor 14 and a ring gear 16 mounted about the rotary kiln l1 and driven by gear 15. The driving power of the driving device 13 is detected by a detector 17 to provide a driving signal which is sent to an integrator 18 which also receives a synchronizing signal from a synchronizing signal generator 19 generating one pulse signal during each one revolution of the kiln for integrating the driving signal for an interval required for the kiln to make one complete revolution. The integrated signal is sent to a memory 20 and is then read out therefrom at each revolution to provide a control signal.

FIG. 2 shows signal diagrams (a), (b) and (c) respectively representing a rotating speed of the kiln, an input power of the driving motor and an output from the in tegrator. These signal diagrams illustrated correspond to several revolutions of the kiln, the driving signal corresponding to one revolution of the kiln having a wavelength as shown in FIG. 3.

The synchronizing signal generator 19 comprises a projection 21 mounted on the periphery of the kiln 11 and a pulse generator 22 operated by the projection for generating one pulse for each revolution of the kiln.

Where the driving motor 14 comprises an induction motor whose speed is controlled by varying the secondary resistance and the effective power of the motor is proportional to the driving torque, the power detector 17 comprises a power detector 23 which detects the effective power in terms of the torque, a speed detector 24 for detecting the rotational speed of the motor 14, and a multiplier 25 for effecting a multiplying operation of the outputs from both detectors 23 and 24, as shown in FIG. 4. The torque detector 23 may be a strain gauge mounted on the motor shaft.

In the case the kiln driving motor 14 comprises a D.C. motor or an A.C. commutator motor, the effective power of the motor may be detected directly by means ofa power detector, as shown in FIG. 5.

As shown in FIG. 6, the memory 20 comprises two capacitors which alternately store and read out the integrated output for each interval required for one revolution of the kiln. More particularly, when a flipflop circuit 201 receives the synchronizing signal to generate signals which open gates 202 and 203 and close gates 204 and 205 (these gates being shown as silicon controlled rectifiers), the output from the integrator is stored in capacitor 206 via enabled gate 202 whereas the signal which has been stored in capacitor 207 is read out through gate 203. When the filp-flop circuit receives the next synchronizing signal the polarity of the output signal from the flip-flop circuit is reversed to store the output signal from the integrator in capacitor 207 via enabled gate 204 and to read out the signal in capacitor 206 via enabled gate 205. The read out signal is sent to a display device, not shown, for informing it to an operator, or an electronic computer, not shown, for effecting the automatic control of the kiln.

Alternate storage and read out of the signals into and out of two capacitors 206 and 207 may be effected by providing a transfer switch to be operated by the projection 21 on the periphery of the kiln for switching the output signal from the integrator at each revolution of the kiln, alternately between two capacitors.

As above described, the kiln driving signals are integrated for the interval corresponding to each one revolution of the kiln, stored in the memory and are successively read out of the memory, thus producing a control signal substantially free from noise component, as shown in FIG. 2(c). Thus, the signal obtained in this manner is not influenced directly by the rotational speed of the kiln so that it is extremely effective to the control of the kiln.This method of driving the control signal can limit the delay of detection to theinterval required for one revolution of the kiln even under the worst condition. Thus, in the ordinary'kiln which is rotated at a speed of one or two revolutions per minute the time delay of the detection is only about one minute or 30 seconds which is of course permissible by considering the phenomena occurring in the rotary kiln.

Where it is necessary to decrease the time delay of the detection the integration of the driving signal may be performed a multiple of two or larger integers for each revolution of the kiln. In this case, the stored signals are read out twice or more than twice for the same interval and the frequency of the synchronizing signal is also increased accordingly.

In the modified embodiment shown in FIG. 7 three axially spaced apart projections 21,, 21 and 21 are mounted on the periphery of the kiln at a circumferential spacing of for generating three pulses from pulse generator 17 during each one revolution of the kiln 11. These pulses are successively applied to integrators 18 18 and 18 respectively, at a spacing corresponding to one-third of one revolution of the kiln, each of the integrator integrating the driving signal from the power detector 20 for an interval corresponding to one revolution of the kiln with a time dealy corresponding to one-third of one revolution. The outputs from the integrators are respectively stored in corresponding memories 20,, 20 and 20 and the signals stored therein are successively read out with a time delay corresponding to one-third of one revolution so as to produce control signals.

FIG. 8 shows a manner for deriving these control signals. As shown in FIG. 8, each integrator integrates the driving signal for the interval of one revolution with a time delay corresponding to one-third of one revolution, and the integrated signals are applied to respective memories from which three control signals are read out during each one revolution of the kiln.

Thus, this modified control system produces a control signal at each one-third revolution of the kiln whereby it is possible to more promptly detect the variation in the internal condition of the kiln than the system shown in FIG. 1 thus rendering the control system to be quick responsive.

Where the control signal requires larger flatness than those of FIGS. 1 and 7 the integrating time may be increased to revolutions equal to multiple of two or larger integers. In such a case it becomes possible to efficiently eliminate large noise components appearing at the time when the rotational speed of the kiln is varied stepwisely. In the control system shown in FIG. 7 where it is desired to increase the flatness of the output signal, the number of integrators may be increased. Thus, for example, for an integrating time of two revolutions, the number of integrating circuits is increased to 6 whereas for an integrating time of three revolutions, the number of integrator isincreased to 9.

, What we claim is:

1. A control system for a rotary kiln comprising:

a driving device for rotating said kiln;

a power detector coupled to said driving device to produce a signal proportional to the power input to said driving device; and

at least one integrator connected to the output of said detector to integrate said signal during at least one revolution of said kiln to produce a noise free control signal.

2. The control system as defined by claim 1 which tor in response to each synchronizing signal.

3. The control system as defined by claim 1 which further includes a store connected to the output of said integrator for storing the integrated driving power signal from said integrator and for transferring the same to an indicator or computer at least one revolution of the kiln.

4. The control system as defined by claim 1 wherein said driving power detector is a strain gauge detecting a strain of the shaft of said driving device, a speed meter detecting the rotational speed of said driving device and a multiplier for multiplying the strain and the rotational speed to obtain the driving signal.

5. The control system as defined by claim 1, wherein said lower detector comprises a power meter for detecting the effective input power of the driving motor which is proportional to the torque.

6. The control system according to claim 2 including a projection mounted on the periphery of said rotary kiln for producing one pulse of said synchronizing generator at each revolution of said kiln.

7. The control system as defined by claim 1 which further includes a synchronizing signal generator, and a plurality of projections mounted on the periphery of said rotary kiln and equally spaced apart from each other in the axial and circumferential directions of said kiln for actuating said generator to produce a plurality of equally spaced apart synchronizing pulses during each revolution of said kiln, and wherein the number of said integrators is equal to the number of said projections, each of said integrators responding to a corresponding synchronizing pulse to integrate the output signal from said power detector for an interval corresponding to one revolution of said kiln at a spacing of l/n where n represents the number of said projections. 

1. A control system for a rotary kiln comprising: a driving device for rotating said kiln; a power detector coupled to said driving device to produce a signal proportional to the power input to said driving device; and at least one integrator connected to the output of said detector to integrate said signal during at least one revolution of said kiln to produce a noise free control signal.
 2. The control system as defined by claim 1 which includes a synchronizing signal generator for generating at least one synchronizing signal during at least every revolution of the kiln, said generator being coupled to said integrator to actuate said integrator in response to each synchronizing signal.
 3. The control system as defined by claim 1 which further includes a store connected to the output of said integrator for storing the integrated driving power signal from said integrator and for transferring the same to an indicator or computer at least one revolution of the kiln.
 4. The control system as defined by claim 1 wherein said driving power detector is a strain gauge detecting a strain of the shaft of said driving device, a speed meter detecting the rotational speed of said driving device and a multiplier for multiplying the strain and the rotational speed to obtain the driving signal.
 5. The control system as defined by claim 1, wherein said lower detector comprises a power meter for detecting the effective input power of the driving motor which is proportional to the torque.
 6. The control system according to claim 2, including a projection mounted on the periphery of saiD rotary kiln for producing one pulse of said synchronizing generator at each revolution of said kiln.
 7. The control system as defined by claim 1 which further includes a synchronizing signal generator, and a plurality of projections mounted on the periphery of said rotary kiln and equally spaced apart from each other in the axial and circumferential directions of said kiln for actuating said generator to produce a plurality of equally spaced apart synchronizing pulses during each revolution of said kiln, and wherein the number of said integrators is equal to the number of said projections, each of said integrators responding to a corresponding synchronizing pulse to integrate the output signal from said power detector for an interval corresponding to one revolution of said kiln at a spacing of 1/n where n represents the number of said projections. 